Filleting volume

 There are three areas of filleting to do on this boat; frame-to-bottom, frame-to-side, and bottom-to-side. The plans call for a 2 inch radius fillet on the frame-to-bottom and the frame-to-side fillets, and a 3 inch radius fillet on the bottom-to-side.

The angle that the panels meet are not perpendicular 90-degree angles. The frame-to-bottom panels vary a little with the curve of the bottom panel fore and aft (the 'rocker'), but they are fairly close to 90-degree. A 2 inch radius fillet looks like the upper-left image in this picture and the cross-section of the epoxy fillet is 0.87 square inches.

 The angle of the bottom-to-side panels is about 20 degrees and remains roughly the same fore to aft. A 3 inch radius fillet looks like the upper-right image in the picture and the cross-section of the epoxy fillet is 0.81 square inches. A larger radius, but the amount of epoxy, although slightly less, is roughly the same as the 2 inch perpendicular fillet.

The angle of the frame-to-side panels varies greatly from fore to aft. Frame #4 is roughly 90 degrees, but the others are significantly different.  Here's frame #1 near the bow, viewed from above.

Frame #1's angle is much more than 20 degrees. The lower-left image in the picture above shows the effect of 20 degrees of angle using the same 2 inch radius on both sides. A huge difference in the cross sectional area, making a huge difference in the amount of epoxy securing each side of the frame. Not just a difference is fillet volume, but also in how far from the corner the fillet extends (glue contact area on the panel).

To alleviate this issue, I will use different radii throughout the frame-to-side fillets. The lower-right image in the top picture shows fillets that are far more equal, but using different radii.

I made myself four filleting squeegees, 3-inch radius, 2-inch radius, 1-1/2 inch radius, and a 1-1/8 inch radius. I then held the squeegees in the frame-side corners and visually selected what looked right. Here is the diagram with the assigned fillet sizes.